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  • 1
    Electronic Resource
    Electronic Resource
    In situ measurement of the rate of H absorption by a Pd cathode during the electrolysis of aqueous solutions (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1324-1330 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental setup to measure "in situ" the amount of H that a Pd cathode absorbs during the electrolysis of aqueous solutions has been built up and tested. The setup implements a volumetric technique, i.e., it involves the measurement of the rate of H2 generation by the cathode. The pros and cons of this type of techniques against other procedures, the measurement of the variation of the cathode electrical resistance or of its dilation during the electrolysis, are briefly discussed. A careful analysis of the setup error sources is done by using two non-H-absorbing Pt electrodes. Neither any significant recombination of the electrolysis gases (H2 and O2), nor any deviation of a 100% electrolysis efficiency have been observed. It has been found that gas (air) release and H2 and O2 absorption by the solution, in the first stage of the electrolysis, seriously affect the measurement of the rate of H absorption by the cathode. Several improvements of the experimental installation and an operation protocol of saturation of H2 and O2 and of exhaustion of air in the solution, before starting the electrolysis, allowed overcoming those limitations. Finally, we present the results obtained in the measurement of the rate of H uptake by a Pd cathode during electrolysis. The reliability of the measurement has been confirmed by electrochemically deloading the Pd cathode. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147901
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  • 2
    Electronic Resource
    Electronic Resource
    Nucleation and growth of pores and photoluminescence in p-type porous silicon (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 866-869 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoluminescence characteristics (peak intensity, peak wavelength and full width at half maximum of the emission band) of p-type porous silicon have been measured as a function of the etching time. Experimental data are discussed in the light of a pore nucleation and growth mechanism recently proposed by the authors. The steps of the formation of the porous layer are clearly apparent in the photoluminescence characteristic evolution. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1489089
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  • 3
    Electronic Resource
    Electronic Resource
    Numerical results for the random field Ising model (invited) (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 3274-3278 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed numerical calculations for the random field (H) ferromagnetic Ising model in two dimensions. To study equilibrium properties, we have used the transfer matrix technique, thus bypassing serious equilibration problems which would arise in a Monte Carlo calculation for random systems. We have calculated the structure factor S vs H. Our results are consistent with S∼exp(c/H2) as predicted by theories which yield a lower critical dimension dc=2, whereas the expected behavior for dc=3, S∼H−4, is inconsistent with our results. To study dynamic properties we have used Monte Carlo simulations to determine the equilibration of Ising systems in random fields at low temperatures T following a quench from high T. The rate at which domains grow with time is determined as a function of the random field strength H, the linear dimension of the system L and temperature T. Domains are found to grow logarithmically with time. For small systems, L≤L*=(4J/H)2, the exponents a and b of the exponential equilibration time τ∼exp[(H/T)aLb] are found to be a(approximately-equal-to)1.0 and b(approximately-equal-to)0.5, in agreement with recent calculations based on approximate interface models. We tested the L and H/T dependence of τ in 3D and found a(approximately-equal-to)1.0, b(approximately-equal-to)0.5 also in 3D.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335123
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  • 4
    Electronic Resource
    Electronic Resource
    Resonant magnetic quantum tunneling through thermally activated states : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6940-6942 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory of the magnetic relaxation of a large spin (S=10) having a large uniaxial magnetocrystalline anisotropy is outlined. The theory explains magnetic relaxation observed in Mn12 acetate. The joint action of local fields and a fourth order distortion of the magnetocrystalline anisotropy is necessary to account for the tunneling that is observed, between the m=−4 and m=4 unperturbed states. Even in resonance, tunneling takes place mainly incoherently in Mn12 acetate. It proceeds through the lowest energy state doublet which is not blocked by longitudinal local fields. The relaxation rate Γ has been calculated using a master equation. The model gives magnetization hysteresis loops and ac magnetic susceptibility curves which are in quantitative agreement with experimental results. For temperatures below 0.5 K approximately, nonresonant tunneling from the ground state becomes the dominant relaxation mechanism. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367554
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  • 5
    Electronic Resource
    Electronic Resource
    Multilayer piezoelectric devices based on PZT (1996)
    Springer
    Journal of materials science 7 (1996), S. 55-60 
    Details
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A PZT 53/47 was obtained by a modified chemical route. Small-particle-size powders were allowed to obtain high solid content, non-aqueous slips with Newtonian behaviour. The use of both the tape-casting technique and the common multilayer ceramic fabrication process led to a high-density multilayer ceramic body without cracks or delaminations, and a homogeneous microstructure. The architecture of multilayer piezoelectrics has an important effect on the clamping of resonance modes, particularly on planar modes, by modifying the nature of the electrode and the effect of the polarization procedure. This fact is corroborated by the dielectric and piezoelectric properties measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00194094
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  • 6
    Electronic Resource
    Electronic Resource
    Nanostructured and near defect-free ceramics by low-temperature pressureless sintering of nanosized Y-TZP powders (1997)
    Springer
    Journal of materials science 32 (1997), S. 4507-4512 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Nanosized (∼6 nm) Y-TZP (3 mol% Y2O3) powders have been produced by chemical co-precipitation (Y-inorganic+Zr-organic precursors) and thorough isopropanol-washing step, after calcining in air at 450°C. The nanocrystalline Y-TZP powders consisted of spherical soft agglomerates (∼100 nm in size) which were easily broken down during compaction resulting in a very uniform green microstructure with a narrow pore size distribution (average pore size less than 6.5 nm) and no detectable compacting defects. In spite of the relatively low green density (43% theoretical), Y-TZP powder compacts sintered to near theoretical density in the very low-temperature range of 1000°C for 80–100 h to 1070°C for 2 h, maintaining a grain size in the nanoscale (〈100 nm) and the sintered bodies were nearly defect-free. Hardly any grain growth took place up to 1000°C; it was very rapid above this temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018613032145
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  • 7
    Electronic Resource
    Electronic Resource
    Improving sintering behaviour of BaTiO3 by small doping additions (1996)
    Springer
    Journal of materials science 31 (1996), S. 975-981 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The dielectric properties of BaTiO3 ceramics are associated with its microstructure, which depends on the stoichiometric ratio, dopant nature, and ceramic processing. Optimum densification at low temperatures to reduce the amount of noble metals in electrodes for Multilayer Ceramic Capacitors (MLC) requires the use of liquid phase sintering. However, depending on the nature and amount of such a liquid phase, exaggerated grain growth is produced. In order to increase the capacitance in BaTiO3-based multilayer capacitors, increasing the dielectric constant by careful and homogeneous development of the microstructure, is necessary. The correct distribution of dopant on the particles' surface leads to a modification of their features by reacting with surface cations such as Ba2+. Such a modification allows densification at low temperatures with very small amounts of liquid phase. As a consequence, good control of grain size is obtained which enhances the dielectric properties of the BaTiO3 ceramics. The controlled microstructure also allows the reduction of the layer width in multilayer arrangements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352898
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  • 8
    Electronic Resource
    Electronic Resource
    An integrated dynamic model for the volcanic activity at Poas volcano, Costa Rica (1987)
    Springer
    Bulletin of volcanology 49 (1987), S. 588-598 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A dynamic model for the activity of Poas Volcano, Costa Rica, is proposed. Data collected during a three-year period show that the volcanic processes occur within a small hydrothermal system. Heat is supplied by a magma body in the conduit and is transferred to the surface by fluid convection. Within a given volume of rock, pore pressure builds up due to the upward motion of fluids and the increase in vapor pressure when the temperature rises above the boiling point. Ultimately, the system becomes unstable when the pore pressure overcomes the total pressure. This leads to the assumption that the kinetic and thermal energies are proportional to the depth at which the mechanical equilibrium is disturbed. Laboratory experiments were performed by heating samples of the crater lake deposits. The preliminary results of these experiments show significant analogies with the low-energy activity of the volcano. Following this model we estimated that a phreatic explosion which reaches 200 m in height (comparable to the one observed by Francis et al. in 1978) originates at a depth of 70 m and a temperature of 180° C; these values agree with those reported in the literature. In addition, “magmatic” sulfur, which partitions into the rising hydrothermal fluids, reacts at lower temperature and higher $$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{f} O_2$$ to produce pockets of liquid sulfur in the conduit deposits and the lava dome. These pockets are subsequently erupted forming the pyroclastic sulfur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01079964
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  • 9
    Electronic Resource
    Electronic Resource
    Off-diagonal long-range order in Little's model (1972)
    Springer
    Journal of low temperature physics 7 (1972), S. 119-127 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Various authors have shown, using nonrigorous arguments, that the one-dimensional model of Little cannot exhibit off-diagonal long-range order (ODLRO) at nonzero temperatures. Hohenberg has proven that ODLRO cannot exist at nonzero temperatures in any one- or two-dimensionalhomogeneous system. Bychkovet al. have shown that the nonhomogeneity in the Little model may produce peculiar forms of ODLRO. Using Bogoliubov's inequality, we prove that such ODLRO vanishes at nonzero temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00629123
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of humidity on the electrical response of porous BaTiO3 ceramics (1999)
    Springer
    Journal of materials science 18 (1999), S. 1297-1299 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006662805186
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